Transcript Plant and Animal Adaptations to Dune and Slack Environments and Human
Plant and Animal Adaptations to Dune and Slack Environments and Human Impacts on Dunes and Slacks
“The beach environment is hostile to plant life”.
Karl E. Graetz, Seacoast Plants of the Carolinas, 1973.
“The environment is an aggregate of extremes and only plants which have a particular constellation of adaptations can survive”.
Paul E. Hosier, Environmental Inventory of Kiawah Island, 1975.
Dune and Slack Environmental Factors
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wind
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salt spray
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unstable substrates
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soil salinity
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soil nutrients
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soil and air temperatures
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soil water content
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saturated and waterlogged soils
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water table fluctuation
Dune and Slack Environment
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factors vary considerably across a dune
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highly dynamic
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location effects species composition
Life-cycle Patterns
Germination Requirements
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scarification
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stratification
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both
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neither trailing wildbean sea elder beach hogwart sea oats (enhanced by stratification) Sea Elder, Iva imbricata
Life-cycle Patterns
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Plants are highly vulnerable during germination and seedling stages
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germination/seedling survival may be determined by its location on the dune (front, top, back)
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soil moisture
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soil and air temperatures
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sand movement
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salt spray
Life-cycle Patterns
Annuals & biennials
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germinate in spring or fall
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spring - trailing wildbean
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fall - cudweed
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poor competitors in the dunes
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maintain high rates of growth for short periods
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produce many seeds
Life-cycle Patterns
Perennials
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sea oats, American beachgrass, sea elder, seaside goldenrod, pennywort
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reproduce vegetatively and from seeds
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dominant dune species tend to reproduce vegetatively from rhizomes
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large lateral spread and/or extensive roots Pennywort, Hydrocotyle bonariensis
Unstable Substrates
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sand movement is a distinctive factor in dune environments
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accumulation or erosion
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moved by wind or water
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sand deposition may be rapid Foredune on Assateague Island, Virginia
Burial....overwash
Burial
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the most distinguishing ecological characteristic of dune plants is their ability to survive burial
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sea oat and American beachgrass growth is stimulated by accumulating sand
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establishment of many plants on the ocean side of foredunes is prevented by sand accumulation examples are cudweed, Canada horseweed, and trailing wildbean
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production of adventitious roots allow plants to adapt to this environmental factor
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seed buried to deeply may not survive
Salt Spray
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impacts distribution of plant species in dune systems
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eliminates salt intolerant species
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many species that can tolerate high levels of salt aerosols are not found on the foredunes, and some species with a low tolerance are found in areas of considerable salt spray
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short life cycle, low profile, low light/ under canopy protection, leaf hairs, thick cuticles Salt spray impact on arborescent plant
Soil Water Content
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low water content in dune soils
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may determine germination and seedling survival of some dune plants
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dune annuals are highly dependent upon rapid uptake of rainfall for survival
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root systems of most dune plants are between 3 and 15 inches deep - often shallow but wide spreading
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some perennials may have roots systems over 24 inches deep - sea elder, seaside goldenrod
Soil Salinity
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sea oats and American beachgrass do not germinate if soil salinity is greater than about 1.0 percent NaCl
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germinate on the dunes, not in low areas occasionally flooded by salt water
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saltmeadow cordgrass is very tolerant of high soil salinity
Soil Nutrients
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dune sand lacking in plant nutrients
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low organic matter and clay content
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basic pH values
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dune plants with extensive rhizome systems can best exploit available nutrients Class holding 20-foot rhizome of Phragmites australis
Water Conservation
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many dune plants have xeromorphic features
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succulent leaves and stems - prickly pear cactus, sea elder
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thick cuticles and epidermal layers - pennywort, seaside goldenrod
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dense hairs or depressed stomata on leaf surface evening primrose, croton
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leaf inrolling reduces evapotranspiration - sea oats, American beachgrass
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C4 pathway for photosynthesis - enhances water conservation - sea oats, bitter panicum
Solar Radiation
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intense solar radiation occurs in dune systems
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limits distribution of plants
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plants respond to sunlight by:
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avoiding radiation - vertical leaf orientation
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solar tracking - shaded pennywort
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increasing surface area - leaf hairs
Saturated & Waterlogged Soils
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characteristic of mesic slacks
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affects plant development - in half- waterlogged soils roots may be confined to the drier soil
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physiological and morphological changes occur in some plants in waterlogged soils Orchardgrass exhibits increased transpiration rates, bulrushes are shorter Wet slack environment, Assateague Island, Virginia
Water Table Fluctuations
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fluctuating water tables are common in slacks
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0.3 - 0.6 meter fluctuations can cause major disturbances in wetland ecosystems
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plants are killed and species change
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dry periods allow for decomposition of organic matter
Plant Adaptations
Waxy, Leathery or Fleshy Leaves
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resist salt damage
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retain moisture
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sea elder
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sea rocket
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yaupon holly
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live oak Yaupon, Ilex vomitoria
Plant Adaptations
Hairs on Leaves
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trap and retain moisture
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resist salt spray
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camphor weed
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croton
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Gaillardia
Plant Adaptations
Inrolled leaves
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minimize dehydration by reducing surface area and preventing water loss from surface pores
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sea oats
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bitter panicum
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saltmeadow cordgrass
Plant Adaptations
Vertically Oriented Leaves
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decrease the exposed leaf surface to the sun
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pennywort
Plant Adaptations
Leaves flattened against the sand
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withstand high winds
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less salt accumulation
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trap sand
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sea purslane
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seabeach amaranth
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euphorbia Seabeach Amaranth, Amaranthus pumilus
Plant Adaptations
Flexible stems and leaf blades
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withstand high winds without breaking
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sea oats
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American beachgrass
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bitter panicum
Plant Adaptations
Succulent Leaves and Stems
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store water to tolerate xeric conditions
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prickly pear cactus
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sea elder
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sea rocket
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Russian thistle Prickly pear cactus, Opuntia humifusa
Plant Adaptations
Climbing or Vine Growth Habits
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enables plants to hug dune or other plants for support against strong winds
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compete for sunlight
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morning glory
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beach pea
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catbrier
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grape Fox grape, Vitis sp.
Plant Adaptations
Extensive Root and Rhizome Systems
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anchor the plant against wind and wave action
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compete for water and nutrients
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continued growth when buried or exposed to the air
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broken rhizomes move with wind or water and establish in another location
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American beachgrass
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sea oats
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bitter panicum
Plant Adaptations
Seed Dispersal
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forcibly ejected
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wind-dispersed
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water-dispersed
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animal trailing wildbean Canada horseweed, cudweed sea rocket, sea elder sandspur, prickly pear cactus Sandspur, Cenchrus tribuloides
Plant Adaptations
Reproductive Strategies
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seed dormancy
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after-ripening - a period of dormancy after dispersal during which seed undergo physiological changes - ex: camphorweed
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high seed production levels
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vegetative - rhizome fragments of American beachgrass root easily
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seeds and/or rhizomes depending on conditions
Plant Adaptations
Symbiotic Relationships
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rhizosphere bacteria and mycorrhizal fungi have been shown to increase the growth and nutrient uptake of dune grasses
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nitrogen-fixing bacteria
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ability to solubilize phosphorous
Plant Adaptations
Facilitative Effects
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Northern Bayberry, a woody nitrogen-fixing shrub, has been shown to have a positive growth effect on American beachgrass and seaside goldenrod growing beneath its canopy
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more shaded
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lower soil temperatures
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higher soil nitrogen levels Bayberry, Myrica pensylvanica
Plant Adaptations
Salt Spray
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killing of terminal leaves and buds results in lateral branching causing a dense canopy to develop and branching away from the salt source
Succession in Dune & Slack Environments
References
Amos, W. H. and S. H. Amos. 1985. National Audobon Society Nature Guides: Atlantic and Gulf coasts. Random House: New York, NY: 670p.
Graetz, K. E., 1973. Seacoast Plants of the Carolinas. U. S. Department of Agriculture Soil Conservation Service, Raleigh, North Carolina, 206 pp.
Environmental Inventory of Kiawah Island, 1975. Environmental Research Center, Inc., Columbia, South Carolina.
Kraus, E. Jean Wilson, 1988. A Guide to Ocean Dune Plants Common to North Carolina. The University of North Carolina Press, Chapel Hill, North Carolina, 72 pp.
Packham, J. R., and A.J. Willis. 1997. Ecology of dunes, saltmarsh and shingle. Chapman and Hall: Cambridge: 335pp. Shumway, Scott W., 2000. Facilitative effects of a sand dune shrub on species growing beneath the shrub canopy. Oecologia (2000) 124: 138 148.
Will, M. E., D. M. Sylvia, 1990. Interaction of Rhizosphere Bacteria, Fertilizer, and Vesicular-Arbuscular Mycorrhizal Fungi with Sea Oats. Appl. Environ. Microbiol., July 1990, p. 2073-2079.
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